Electric furnace.



No. 82,788. PATENTED MAR. 24, 1908. A. L. MARSH.-

ELECTRIC FURNACE.

APPLIGATIOH FILED SEPT. 19, 1907.

InuanZ-o 7 x UNITED sTATEs PATENT oEEIoE- ALBERT L. MARSH, OF LAKE BLUFF, ILLINOIS, ASSIGNOR TO HOSKINS COMPANY, OF

- CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

ELE CTBIC FURNACE.

Specification of Letters Patent.

Patented March 24, 1908.

Application filed September 19, 1907. Serial No. 393,730.

' Improvement in Electric Furnaces, of which the following is a specification.

The object of my invention is to provide a novel construction of electric furnace whereby the intensity of heating the resister shall be rendered regulable by forming .it of surface-contacting sections and e uipping it with means for compressing t e sections together and varying the degree of com' pression at will to vary accordingly the resistance.

In the accompanying drawings, Figure 1 shows my improved furnace, in one form of embodiment of the invention, by a vertical section, partly in elevation, and Fig. 2 is a plan View of the same.

The particular construction of the furnace illustrated in the drawing represents one of various forms of embodiment of my invention of'which it is susceptible, all of which are intended to be included as within the same. The essence of my invention, however, lies in adapting the principle of variable electric resistance, under variation in contact-pressure of the sections of a sectional resistor, to produce a contact-resistance type of electric furnace.

In'the drawings, which present my improved furnace in cylindrical shape, 3 is the casing of insulating material, as magnesite, fire-brick, or the like, having a closed base and an open top provided with 'a disk-shaped cover 4, which may be composed of asbestos-board, the cover being securely but removably fastened in'place by bolts 5 passing through the wall of the casing to project beyond its upper end through openings in the cover near its edgeto receive nuts 6 to be screwed down against the cover. The wall and base of the casing are reinforced by a sheet-metal sheathing 7, and the casing is shown to be supported on legs 8 between which depend from the bottom of the sheathing rigid arms 9 converging to aline with a central opening 10 provided in the casing-base, these arms containing at their junction a stationary nut 11 in which works a screw 12 against a bearing 13. In the casing is contained the resistor 14,'forming the furnace lining, made up of separate contacting solid pieces or sections 15 of suitable material, preferably carbon, though' they may be of surface-oxidized metal, or

compounds of metals, such as the oXids and sulfids of metals which are conductors of electricity at ordinary temperatures, the end sections 16 and 17 being. preferably composed of graphite and having terminalposts 18 and 19, of the same material, pro

jecting from them, respectively. As shown, the sections .15 and 16 are in the form of flat annular plates or rings, the upper section 16 being thicker than the sections 15, but like the section 17 in thickness though not annular, being a disk shaped block; and it seats on the inner surface of the casingbase, through the central opening in which its terminal-post 19 passes to engage at its lower end with the bearing 13. The bodies forming the resistor-sections conform to and fit within the casing 3, composing a pile or stack therein confined between the casingbase and cover 4, through an eccentric open.- ing 20 in which the terminal-post 18 of the upper section 16 protrudes. The rings 16, 17

form a wall or heating chamber 21,Twith which a central opening 22 in the cover coincides through which to introduce a crucible (not shown) the contents of which are to be subjected to the furnace heat. The section 17 affords a closing head .to the furnace-chamber.

The leads for conducting electrical current-supply of suitable voltage and power to and from the furnace are shown at 23 and 24,

each terminating in a metal (copper) sleeve 25, one to fit closely about the upper post 18 and the other to fit similarly about the post 19.

By turning the screw 12 in one direction or the other the register-sections, which are compressed between it and thecover 4, will be loosened or tightened as to their surfacecontact with ,each other, to increase or decrease the resistance for regulating the intensity of heating the furnace, which the nicety.

The electrical resistance of the resister sections varies inversely as the pressure, so that the screw 12, or any other suitablemedium for regulating the degree of com ression, affords a ready medium of 'contro ling the heat of the furnace.

As advantages of the contact-resistance construction enables to be performed -to a p furnace thus described over the known solidcarbon resister type, the following may be mentioned: Greater resistance per unit of length for a given cross-section of resister; lesser sensitiveness of the furnace to reduction in cross-section of resister due to buming, since the resistance depends more on the number of sections in series and the pressure than on the area of contact; the furnace-resister is more durable under heat, since a larger cross-section may be used for a iven resistance in the furnace and the time 0 consumption of the resister is lengthened; the

'furnace is of non-fra ile construction, differing in that respect rom a solid-carbon resister, which is liable to fracture andthus break the circuit, whereas in my contact-' section construction the cracking of one or more of the plates or blocks makes little, if any, difference in the operation of the furnace; and, finally, the resistor is more readily renewed when burned out, the sections merely being required to be dropped. into place and the regulating screw turned up, while the solid-carbon resistor, which is a mere rod, must be carefully adjusted in place and connected in a manner to avoid the exertion of torsional or breaking strains upon it.

My improved t e of furnace has a great advantage over t e' known granular-carbon resister in starting it or bringing u the heat, and in the matter of regulation a 'ter attaining the proper high temperature. The resistance in the granular-carbon type of furnace is very high 'when the furnace is cold and much lower when it is at white heat; therefore, with a sin le voltage which is right for the furnace at ull heat, the furnace is slow of heating, since the power put in is small until the high temperature is attained.

petvfieen said bodies, for the purpose set ort 2. An electric furnace, the lining of which forms a variable-resistance rheostat constituting the furnace-resister, said linin consisting of contactin bodies of solid e ectroconductive material in series, and a compression-device working against said series of bodies endwise thereof to increase and decrease the pressure-contact between them, for the purpose set forth.

3. An electric furnace, the lining of which forms a variable-resistance rheostat constituting the' furnaceresister, said linin consisting of flatwise contacting rings of e ectroconductive material and a head of similar material, with compressing means for the lining adapted to increase and decrease the pressure-contact between the sections thereof, for the purpose set forth.

4. Anelectric furnace having a casing of insulating material provided with a sheathing of metal and the lining of which forms a variable-resistance rheostat constituting the furnace-resistcr, said lining consistin of a series of fiatwise-contacting rings of e eetroconductive material and a head of similar material, a cover on said casing, and a com- )ression-scrcw working against said head, for the purpose set forth.

5. In an electric furnace, the combination of a resister composed of a series of contacting rings of solid carbonaceous material forming the furnace-chamber provided with a head of similar material having a terminalpost extending from it, the outer ring of said series having a similar post, said posts affording lead-connections with the resistor, a metal-sheathed casing of insulating material inclosing said resister, and through the base of which the terminal-post on said head protrudes, a cover removably secured on said casing and through which the other termina -post protrudes, legs sup orting the furnace, arms depending from the casing, a nut supported by said arms, a screw working in said nut, and a bearing supported to be engaged by said screw and form ng a seat for the terminal-post on said head, for the purpose setforth.

- ALBERT L. MARSH.

In presence of W. T. Jonas, R. A. Sonanrna. 

